Image pickup apparatus

ABSTRACT

An image pickup apparatus comprises: an image sensor for converting an optical image into distribution information of a minority carrier; a control circuit for periodically forming a first state in that a majority carrier is accumulated in the image sensor and a second state in that at least a part of the minority carrier is recombined with this majority carrier; a readout circuit for reading out the information in the image sensor; a recording apparatus for selectively recording the information for a predetermined interval from the information to be read out by the readout circuit with regard to the trigger operation for a still photograph; and a stopping circuit for stopping the control operation of the control circuit in association with the start of the recording by the recording apparatus or the closing of a shutter or in response to a low luminous condition or the like.

FIELD OF THE INVENTION

The present invention relates to an image pickup apparatus which caneffectively suppress the blooming.

BACKGROUND OF THE INVENTION

Generally, in solid state image sensors such as a CCD or the like, therehas been considered a method whereby an overflow drain is provided inthe photosensing surface to prevent the blooming or the overflowcarriers are extinguished using the surface recombination.

In particular, the latter method is known by, for example, UnitedKingdom Patent Publication Gazette GB No. 2,069,759A (applicant, N. V.Philips; inventors, Marnix Guillaume Collet et al), and the like. Such amethod has advantages such that sensitivity is high since an aperture inthe photosensing surface is not sacrificed and that horizontalresolution is raised since the integration degree can be improved, andthe like.

FIGS. 1-3 show diagrams to describe such a method of preventing theblooming by the surface recombination, in which FIG. 1 shows a frontview of an ordinary frame transfer type CCD.

In the drawings, a reference numeral 1 denotes a photosensing partconsisting of a plurality of vertical transfer registers havingphotosensitivity.

On the other hand, a numeral 2 indicates a storage part consisting of aplurality of vertical transfer registers which are shielded against thelight. 3 represents a horizontal transfer register which simultaneouslyshifts the information in the respective vertical transfer registers ofthe storage part 2 by one bit, thereby taking them in this horizontaltransfer register. The register 3 then performs the horizontal transferoperation so that a video signal can be obtained from an outputamplifier 4.

Generally, the information formed in each vertical transfer register ofthe photosensing part 1 is vertically transferred to the storage part 2in the vertical blanking interval in the standard television system andis sequentially read out on a line by line basis by the horizontaltransfer register 3 in the next vertical scanning interval.

The photosensing part 1, storage part 2 and horizontal transfer register3 are respectively two-phase driven and their respective transferelectrodes are indicated by P₁, P₂, P₃, P₄, P₅, and P₆ and the transferclocks are represented by φ_(P1), φ_(P2), φ_(P3), φ_(P4), φ_(P5) andφ_(P6) respectively.

FIG. 2 is a diagram showing a potential profile under such transferelectrodes P₁ -P₆. Low-potential portions and high-potential portionsare formed under the respective electrodes provided on, for example, ap-type silicon substrate 6 through an insulating layer 5 by way of ionimplantation or the like. For example, when a low-level voltage -V₁ isapplied to the electrodes P₂, P₄ and P₆ and a high-level voltage V₂ isapplied to the electrodes P₁, P₃ and P₅, the potentials such asindicated by the solid lines in FIG. 2 are formed. On the other hand,when the low-level voltage -V₁ is supplied to the electrodes P₁, P₃ andP₅ and the high-level voltage V₂ is supplied to the electrodes P₂, P₄and P₆, the potentials such as indicated by the broken lines in FIG. 2are formed.

Therefore, by applying the alternating voltages having opposite phasesto each other to the electrodes P₁, P₃, P₅ and to the electrodes P₂, P₄,P₆ the carriers are sequentially transferred in one direction (to theright in the drawing).

In addition, the alternate long and short dash lines in FIG. 2 show thepotentials when a large positive voltage V₃ is applied to theelectrodes. Since the wells of these potentials are in the invertingstate, the overflow carrier of not smaller than a predetermined amountwill have been recombined with the majority carrier and will beextinguished.

FIG. 3 is a diagram showing such a relation between the electrodevoltage and the shape of the interval potential with respect to thedirection of thickness of the semiconductor substrate 6. It can be seenfrom FIG. 3 that the potential well for the electrode voltage V₃ isshallow, so that the overflow carrier is in a second state in that it isrecombined with the majority carrier at the interface with theinsulating layer.

On the other hand, the potential state becomes the accumulation state asa first state at the electrode voltage -V₁, so that the majority carrieris easily collected around the interface; for example, this majoritycarrier is supplied from a channel stopper region (not shown).

Therefore, by alternately applying the voltages -V₁ and V₃ to theelectrode P₁ in the state in that a carrier is formed by, for example,applying the voltage -V₁ to the electrode P₂, the minority carrier to beaccumulated under the electrode P₁ is limited to not larger than apredetermined amount.

However on the contrary, to effectively extinguish the overflow carrier,the accumulation state and the inverting state have to be alternatelyformed at a high speed in the semiconductor substrate in theaccumulating interval; therefore, this causes a problem such thatelectric power consumption is large. In addition, if such a pulsecontrol is performed at high speed, there will be also caused a problemsuch that the noise to be caused by this pulse is mixed with the signal.Also, there is a problem such that the dark current drift may easilyoccur due to such a pulse.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an image pickupapparatus which can solve such drawbacks in conventional technology.

Another object of the invention is to provide an image pickup apparatuswhich can effectively prevent the blooming and which has a high electricpower saving effect.

Still another object of the present invention is to provide an imagepickup apparatus which can eliminate the noise upon recording.

In addition, it is a further object of the present invention to providean image pickup apparatus having a higher electric power saving effectin a system which can shield a photosensing part against the light by ashutter.

Another object of the invention is to provide an image pickup apparatushaving a high electric power saving effect and a high noise preventingeffect in a system which forms an image signal of one picture by atrigger signal.

A further object of the present invention is to provide an image pickupapparatus which enables the optimum prevention of the blooming inresponse to the state of an object to be photographed.

The above and other objects, features and advantages of the presentinvention will be apparent from the following detailed description inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing an example of an image sensor;

FIG. 2 is a diagram showing an example of a potential profile under eachelectrode;

FIG. 3 is a diagram showing potential characteristics in accordance withthe electrode potentials;

FIG. 4 is a diagram showing the construction of a first embodiment of animage pickup apparatus of the present invention;

FIG. 5 shows drive timing charts for the embodiment shown in FIG. 4;

FIG. 6 is a diagram showing the construction of a second embodiment ofthe image pickup apparatus of the present invention;

FIG. 7 shows drive timing charts for the embodiment shown in FIG. 6;

FIG. 8 is a diagram showing an example of the construction in which apart of the embodiment shown in FIG. 6 is changed;

FIG. 9 is a diagram showing a third embodiment of the image pickupapparatus of the present invention;

FIG. 10 shows timing charts therefor;

FIG. 11 is a diagram showing a fourth embodiment of the presentinvention;

FIG. 12 is a diagram showing a fifth embodiment of the presentinvention;

FIG. 13 is a diagram showing a sixth embodiment of the presentinvention;

FIG. 14 is a diagram showing a seventh embodiment of the presentinvention;

FIG. 15 is a diagram showing an eighth embodiment of the presentinvention; and

FIG. 16 is a diagram showing a ninth embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will be described in detail hereinbelow withrespect to its preferred embodiments.

FIG. 4 is a diagram showing a first embodiment of the construction of animage pickup apparatus of the present invention and FIG. 5 shows timingcharts therefor, in which a reference numeral 100 denotes an imagesensor as image pickup means. This image sensor may be a CCD such asshown in FIG. 1 or may be an XY address image sensor of the MOS type.

In this embodiment, the case will be described where the frame transfertype CCD shown in FIG. 1 is used.

A reference numeral 7 represents a driver circuit as readout means forsupplying transfer pulses φ_(P1) -φ_(P6), which are necessary for thetransfer of information from this CCD image sensor, and an anti-bloomingpulse φ_(AB) which will be described later. Numeral 9 is a first clockgenerator as a clock signal source for forming timing signals of φ_(P1)-φ_(P6) among these pulses. Numeral 8 is a second block generator asrecombination means and the driver circuit 7 forms the anti-bloomingpulse φ_(AB) in response to the timing signal from this clock generator8 and supplies it to the electrode P₁ or P₂ of the image sensor.

After the output of the image sensor 100 is amplified by an amplifier10, it is subjected to the γ-compensation, aperture-compensation, etc.in a processor 11 and is introduced through a gate 12 to a head 13 andis recorded in a recording medium 14. The head 13, medium 14, etc.constitute recording means. The output of the gate 12 may be suppliednot only to the recording means but also to, for example, a transmittingapparatus, printer, or the like.

A reference numeral 19 is a trigger circuit as trigger means for forminga pulse signal by operating an operating switch TB. This trigger circuitis provided to selectively perform the recording, transmission,printing, or the like of the image of one field or one frame as will bedescribed later by operating this operating switch TB at a proper timingwhile, for example, observing the output of the processor 11 by a videomonitor. As shown in FIG. 5, a high-level signal is output from aone-shot circuit 18 for only a predetermined interval (e.g., onevertical sync interval) synchronously with the trailing edge of thepulse output from the trigger circuit 19.

Numeral 16 is a one-shot circuit for outputting a high-level pulse for apredetermined interval synchronously with the trailing edge of avertical sync pulse V_(D) from the clock generator 9. The output of thisone-shot circuit 16 is input to a clock input terminal of a D-flip-flop.

Therefore, as shown in FIG. 5, the gate 12 is open for an interval oftime from a time point t₁ when the first vertical sync signal V_(D) wasobtained after the trigger pulse from the trigger circuit 19 had beenoutputted to a time point t₃ when the next vertical sync signal isobtained. Thus, the signal of one field is recorded in the recordingmedium 14 through the head 13. The recording medium 14 is driven by amotor MT which rotates synchronously with the phase of the vertical syncsignal.

On the other hand, while this gate 12 is open, the output of the secondclock generator 8 is stopped through an inverter 20. A control block 15comprises of the one-shot circuits 16 and 18 and flip-flop 17.

Furthermore, as shown in FIG. 5, the anti-blooming pulse φ_(AB) is madeinoperative during the vertical transfer intervals t₁ -t₂, t₃ -t₄, t₅-t₆ and t₇ -t₈.

Also, the pulse φ_(AB) is switching controlled by the driver 7 so as tobe alternately added to the pulse φ_(P1) or pulse φ_(P2) for everyfield. In addition, the phases of the pulses φ_(P1) and φ_(P2) areshifted by only one field; therefore, the locations of the potentialwell and potential barrier are shifted by only the amounts correspondingto the electrodes P₁ and P₂ for every field. Due to this, theinterlacing is performed. The pulse φ_(AB) is added to the electrodewhich does not form the potential barrier, i.e., to the electrode whosepotential is 0 level in case of FIG. 5.

In addition, in this embodiment, although the formation of the pulseφ_(AB) is stopped for only the interval when the output of the imagesensor is being recorded, it may be possible to form the pulse φ_(AB)for only a proper period of time, e.g., a few V (vertical intervals)after the recording was started.

In this way, since there is an operating time lag until the nextrecording operation is done after the previous recording operation wasfinished, a larger electric power saving effect will be obtained if asystem is constituted so as to stop the pulse φ_(AB) for only apredetermined time after the recording was started as described above.

In addition, although the case has been described where only one fieldin the video signal to be formed continuously is extracted and isrecorded in this embodiment, the present invention is of courseeffective in a construction in which the image sensor is exposed for apredetermined time by a shutter or the like and thereafter the pictureimage on this image sensor is read out and is recorded for example asthe image information of two fields which were mutually interlaced.

Moreover, in this embodiment, φ_(AB) is set into 0 level and is madeinoperative for only a predetermined time after the recording wasstarted by opening the gate 12; however, it may be possible to apply thepotential of for example -V₁ in this interval except the verticaltransfer interval. In this case, an effect such that the dark current isdifficult to be generated is produced.

As described above, in this embodiment, the supply of the high-frequencypulse for the anti-blooming is stopped in association with the startingof the recording of the signal output to be read out from the imagepickup means; therefore, it is possible to save an electric powerconsumption. Moreover, the blooming is difficult to be caused in thevideo signal to be recorded.

On the other hand, since the noise caused due to the pulse for theabove-mentioned anti-blooming is not generated during the recording, anS/N ratio of the recording signal does not deteriorate.

Next, FIG. 6 is a diagram showing a second embodiment of the imagepickup apparatus of the present invention and FIG. 7 shows timing chartstherefor. In FIGS. 6 and 7, the same elements as those in FIGS. 1-5 aredesignated by the same reference numerals. This embodiment shows thecase where a shutter 628 is provided in front of the image sensor 100.

In this embodiment, the output of the one-shot circuit 16 and the outputof the one-shot circuit 18 are input to an AND gate 620.

Therefore, as shown in FIG. 7, a high-level signal is output from theAND gate 620 synchronously with the trailing edge of the first verticalsync signal V_(D) after the trigger pulse was outputted. A referencenumeral 617 denotes a timer for specifying the exposure time by theshutter 628. When the high-level signal is inputted from the AND gate620, the timer 617 outputs a high-level pulse at a time point when atime Ts which was set by a setting resistor 622 has passed after thetrailing edge of that high-level signal.

Numeral 621 is a timer for outputting a high-level signal for only apredetermined time in response to this pulse. The shutter 628 is closedfor this high-level signal interval in response to the output from ashutter control circuit 627.

The shutter 628 is energized ordinarily by a spring and the like so asto be opened.

In addition, the second clock generator 8 is controlled so as to bestopped by an inverter 626 during the interval when this shutter isclosed.

This inverter 626 and the timer 621 constitute stop means according tothe present invention.

The output of a one-shot circuit 624 for forming a pulse synchronouslywith the leading edge of the timer 621 and the output of the one-shotcircuit 16 are supplied to a timer circuit 625 through an AND gate 623.

The timer circuit 625 is the circuit for outputting a high-level signalsynchronously with the leading edge of the input signal for only, e.g.,1 V (vertical interval) and opens the gate 12 during only thishigh-level interval.

Thus, the recording is started synchronously with the first verticalsync signal after the shutter was closed and the signal for one fieldinterval is recorded.

On the other hand, the formation of the pulse φ_(AB) is stopped for onlythe interval when the light incidence to the image sensor 100 is blockedby the shutter 628 in this embodiment; however, it may be possible tostop the pulse φ_(AB) for only a proper time, e.g., a few V (verticalinterval) after the closing of the shutter was started.

FIG. 8 is a diagram showing such an embodiment. In this embodiment, theoutput of the timer circuit 621 is inputted to the shutter controlcircuit 627 and is used for the opening and closing controls of theshutter 628, and at the same time it is inputted to a timer circuit 629.This timer circuit 629 outputs a high-level signal for a predeterminedtime (e.g., a few V intervals) after the leading edge of the output ofthe timer circuit 621.

The output of this timer circuit 629 is inputted to the clock generator8 through the inverter 626.

Therefore, once the output of the timer circuit 621 rises, it ispossible to disable φ_(AB) irrespective of the opening/closing of theshutter 628.

Since there is a time lag with regard to the operation until the nextimage pickup operation is further performed after the recordingoperation was carried out upon completion of the image pickup operationusing the shutter, if a system is constructed in a manner such that thepulse φ_(AB) is stopped for only a predetermined time after the closingof the shutter was started as described above, a larger electric powersaving effect will be obtained and will be actually useful.

As described above, according to the second embodiment, the shutter forblocking the light incidence to the image pickup means is provided,thereby making the exposure time control possible to this shutter andenabling the smear during the vertical transfer interval to beprevented, and at same time while at least the light incidence isblocked by this shutter, the pulse φ_(AB) for the anti-blooming is notformed; therefore, the electric power to be consumed can be remarkablysaved.

In addition, since almost only the dark current exists while the shutteris closed, no blooming occurs; on the other hand, while the shutter isopen, the overflow carrier is extinguished by the pulse φ_(AB), so thatthe blooming is effectively suppressed.

The dark current drift and noise are certainly reduced while the pulseφ_(AB) is stopped, so that the recording signal and the like are notadversely affected.

Now, FIG. 9 is a diagram showing a third embodiment of the presentinvention and FIG. 10 shows timing charts therefor, in which the sameelements as those shown in FIGS. 1-8 are designated by the samereference numerals. In FIG. 9, a reference numeral 926 denots an RSflip-flop which is set in response to the leading edge of the output ofthe AND gate 620 and is reset responsive to the leading edge of theoutput of the timer 617. The Q output of this RS flip-flop controls theon-off operations of the second clock generator 8. Namely, when the Qoutput is high, the generator 8 is turned off and when the Q output islow, it is turned on.

According to this embodiment, the recombination control means forpreventing the blooming is made operative only for the interval when thepicture image information to be selected by the selecting means is beingaccumulated by the image sensor, so that the electric power to beconsumed can be extremely reduced.

In addition, since the dark current drift and noise are decreased whilethe pulse φ_(AB) is stopped, the recording signal and the like are notadversely influenced.

On one hand, in the second and third embodiments, since the shutter 628is closed even while the signal selected by the gate 12 is beingrecorded or the like, there is not a fear of mixture of the bloomingnoise on the next screen into the above-mentioned signal selected.

Although the exposure time control and the prevention of the smearduring the vertical transfer interval are performed by the shutter inthis embodiment, the present invention can be of course applied to asystem using no shutter.

Next, FIG. 11 is a block diagram showing a fourth embodiment of theimage pickup apparatus of the present invention. In the drawing, a lightfrom an object to be photographed passes through an optical systemindicated by 407 and a diaphragm 408 disposed on the optical paththereof. This incident light is formed on the image sensor 100 such as,for example, a CCD or the like as shown in FIG. 1 and at the same timeit enters a photometric photosensing device 414 through a beam splitter409 and a deflecting mirror 413.

The photosensing device 414, an operational amplifier 427 and a resistor426 constitute a well-known photoelectric converter. In addition, aresistor 428, a resistor 429, an operational amplifier 431, and areference voltage source 430 which are connected to the output of theoperational amplifier 427 constitute an inverting amplifier forcomparing the output from the operational amplifier 427 with thereference voltage source 430 and inverting and amplifying it. The outputthereof is connected to one input terminal of an OR gate 422 and at thesame time it is connected to a driving coil 432 for driving thediaphragm. The diaphragm driving coil 432 serves to open the diaphragm408 when a positive voltage is applied by the operational amplifier 431and to close the diaphragm 408 when a negative voltage is applied. Theoutput of the image sensor 100 is connected to a luminance separatingcircuit 411 and the output of the circuit 411 is further connected to anintegrating circuit 412 and a peak-hold circuit 418, respectively. Theoutput of the integrating circuit 412 is connected to an inverting inputof a comparator 416 and a non-inverting input of the comparator 416 isconnected to a reference voltage source 417. The output of thecomparator 416 is connected to one input of an AND gate 421. Theintegrating circuit may be a smoothing circuit, mean value circuit orlow-pass filter. The output of the peak-hold circuit 418 is connected toan inverting input of a comparator 419 and a non-inverting input of thecomparator 419 is connected to a reference voltage source 420. Theoutput of the comparator 419 is connected to the other input of the ANDgate 421. The output of the AND gate 421 is connected to the other inputof the OR gate 422. The output of the OR gate 422 is connected to acontrol terminal of a switching circuit 436. The output of the peak-holdcircuit 418 is connected to a voltage controlled oscillator 424 throughthe switching circuit 436. The output of the voltage controlledoscillator 424 is connected to a driver 434 for forming a driving pulseof the CCD 100. A reference numeral 435 is a clock generator foroutputting timing signals of various pulses to drive the CCD 100.

The driver 434 outputs the pulses φ_(P1) -φ_(P6) in response to thesetiming signals.

On the other hand, the driver 434 forms the alternating pulse φ_(AB)which changes between the voltages -V₁ and +V₃ in FIG. 3 in response tothe output of the voltage controlled oscillator 424 and supplies thispulse φ_(AB) to the CCD.

Numeral 437 indicates a setting value circuit connected to the b side ofthe switching circuit 436. While a high-level signal is output from theOR gate 422, the contact of this switching circuit 436 is switched tothe b side in response to this high-level signal, so that apredetermined set value V₀ is input to an input terminal of the voltagecontrolled oscillator 424. The set value is for example 0 (volt) and theoscillator 424 is constituted in a manner such that the oscillatingfrequency is zero, namely, the oscillation is stopped for the 0-voltinput.

In addition, the circuits 412, 416, 418-420, 422, 414, 426-431, etc.constitute object information detecting means for forming informationwith respect to the brightness or the like of the object. Also, thecircuits 424, 436, 437, etc. constitute second control means forcontrolling the recombination state in response to the signal from thisforming means.

The operation of the embodiment shown in FIG. 11 will now be described.In the case where the amount of light incident into the photosensingdevice 414 is smaller than a appropriate value, the output of thephotoelectric converter becomes low voltage, so that the output of theinverting amplifier 431 becomes positive high voltage. Therefore, thepositive voltage is applied to the diaphragm driving coil 432, so thatthe diaphragm is driven so as to be open. On the contrary, in the casewhere an amount of light incident into the photosensing device 414 islarger than the appropriate value, the opposite operation to the aboveis performed, so that a current flows through the diaphragm driving coil432 in the direction such as to close the diaphragm, thereby reducingthe light incident amount.

On the other hand, the object image formed on the image sensor 100 isphotoelectric converted and the charge information is formed in theimage sensor 100. The luminous component is separated from the output ofthe image sensor 100 by the luminance separating circuit 411 and isintegrated by the integrating circuit 412, thereby detecting the meanluminous level of the object.

The comparator 416 compares this level with a predetermined referencelevel and when the output of the integrating circuit 412 is lower thanthe predetermined level, a high-level signal is outputted from thecomparator 416.

Namely, when the mean luminous level of the object is lower than that bya certain value, a high-level signal is obtained from the comparator.

On one hand, the output of the luminance separating circuit 412 isconnected to the peak-hold circuit 418, thereby detecting the peak inthe luminance signal. The comparator 419 compares the peak thus detectedwith the voltage of the reference voltage source 420 and when the peaklevel is lower than that, a high-level signal is outputted. Only in thecase where both outputs of the comparators 416 and 419 are at highlevel, i.e., only when the mean luminance of the object is low and thehighest luminance is also low, the AND gate 421 outputs a high-levelsignal and the OR gate 422 also outputs a high-level signal, so that theswitch 436 is switched to the b side, thereby stopping the oscillationof the voltage controlled oscillating circuit 424.

In addition, since the outputs of the integrating circuit 412 andpeak-hold circuit 418 are delayed by only the output scanning time ofthe image sensor 100 and at the same time the time lag to be caused dueto the diaphragm (stop) adjusting operation is further added to thoseoutputs, in the case where the light incident into the photosensingdevice 414 is too weak as a result of that, for example, the diaphragmwas adjusted to be too narrow, namely, in the case where a positivevoltage is applied to the diaphragm driving coil 432 and it is driven soas to open the diaphragm, a high-level signal is inputted to the OR gate422, so that the OR gate 422 outputs a high-level signal. Consequently,the oscillation of the oscillator 424 is stopped similarly as describedbefore.

In the state where this oscillation was stopped, the image sensor 100 isordinarily periodically driven by the pulses φ_(P1) -φ_(P6) shwon inFIG. 1 and φ_(AB) is not added.

Furthermore, when the output of the OR gate 422 is at low level, theoutput of the peak-hold circuit 418 is inputted to the voltagecontrolled oscillator 424 through the switch 436 and the oscillator 424generates the pulse train of higher frequency in response to the peakvalue as the peak value is larger, so that the pulse φ_(AB) inaccordance with that pulse train is supplied to the image sensor 100.

In addition, in this embodiment, when a power supply (not shown) isturned on, the pulses φ_(P1) -φ_(P6) are always supplied at the cycle inaccordance with an ordinary standard television system and at the sametime its pulse voltage is set so as to change between -V₁ and +V₂ inFIG. 3.

Also, the pulse φ_(AB) is supplied to the transfer electrodes of theimage sensor by being added to these pulses φ_(P1) -100 _(P6).

Moreover, the pulse φ_(AB) is controlled by the driver 434 so as to beat 0 level while the charge information in the photosensing part 1 ofthe image sensor 100 is being vertically transferred to the storage part2. Therefore, φ_(AB) does not disturb the vertical transfer.

As described above, according to the present invention, an object imageis converted into charge information by the image pickup means, thischarge information is read out to obtain a luminance signal, and thefrequency of the recombination pulse of the charges is controlled independence upon the peak level of this luminance signal; therefore, itis possible to effectively utilize the electric power necessary forrecombination.

In addition, in this embodiment, in the case where the average level ofthe luminance signal is smaller than a predetermined level and at thesame time when the peak level of the luminance signal is smaller than apredetermined level, the formation of the pulse φ_(AB) for recombinationis stopped; thus, this enables unnecessry electric power consumption tobe effectively reduced.

Moreover, since the pulse φ_(AB) is also stopped in the case where thephotometric output of another photometric device other than the imagepickup means is smaller than a predetermined level, even in the casewhere, for example, a picture plane is suddenly switched from a brightobject to a dark object, or the like, unnecessary pulse φ_(AB) can beomitted with high response speed.

On the other hand, in this embodiment, although the oscillatingfrequency of the voltage controlled oscillator (VCO) 424 is changed inaccordance with the output of the peak-hold circuit 418, i.e., with thepeak value of the luminance signal, it may be possible to control theoscillating frequency of the VCO 424 in dependence upon the output levelof the integrating circuit 412 of FIG. 11 as a fifth embodiment as shownin FIG. 12. In this case, the frequency of the VCO 424 may be set to behigh in dependence upon an increase in the output of the circuit 412.

Or as shown in FIG. 13 as a sixth embodiment, by connecting thephotosensing device 414, operational amplifier 427 and a diode 260 forlogarithm compression as shown in the drawing, the logarithm compressionvalue responsive to the incident light amount into the photosensingdevice is outputted and the frequency of the pulse φ_(AB) may becontrolled depending upon the logarithm of the incident light amountinto the photosensing device 414 by inputting this output value to theVCO 424.

This frequency φ_(AB) is controlled so as to become high in response toan increase in the incident light amount in the similar manner as in thefourth and fifth embodiments.

In addition, the photosensing device 414 may be the device for measuringthe TTL (Through The Lens) light or the device for measuring the outsidelight.

On the other hand, the oscillating frequency of the VCO 424 may becontinuously controlled in the 4th-6th embodiments and the frequency maybe changed step by step by being divided into several stages.

These 5th and 6th embodiments allow the construction to be simplified.

FIG. 14 is a diagram showing a seventh embodiment of the presentinvention, in which an oscillator 438 for forming the pulse φ_(AB) forrecombination of constant frequency by the driver 434 is provided inplace of the oscillator 424 shown in FIG. 11, thereby stopping thisoscillator 438 while the output of the comparator 431 shown in FIG. 11is at high level.

Although not shown, even in this case, the output of the photosensingdevice 414 shown in FIG. 11 is inputted through the resistor 428 to thecomparator 431 and this photosensing device 414 may be the device formeasuring the outside light.

FIG. 15 is a diagram showing an eighth embodiment of the presentinvention, in which the on-off operations of the oscillator 438 in the7th embodiment are performed by the comparator 416 shown in FIG. 11, andthe oscillator 438 is turned off while the comparator 416 outputs ahigh-level signal.

FIG. 16 is a diagram showing a ninth embodiment, in which the oscillator438 of FIG. 15 is turned off while the output of the comparator 419shown in FIG. 11 is at high level.

As described above, in the embodiments shown in FIGS. 14-16, theoscillation of the pulse φ_(AB) is turned off in any of the cases wherethe output of the photosensing device is lower than a predeterminedlevel, where the mean value of the luminance signal is lower than apredetermined level, and where the peak value of the luminance signal islower than a predetermined level; therefore, a high electric powersaving effect is obtained and a circuit constitution is also simplified.

As described above, according to these embodiments, the oscillatingfrequency of the pulse for recombination is controlled in apredetermined range including zero in accordance with the state of theluminance of an object (for example, output level of the photosensingdevice, average level of the luminance signal, peak value of theluminance signal, etc.), so that the electric power in association withthe formation of the pulse for recombination can be effectively savedand at the same time there is an effect such that the blooming isdifficult to be caused. That is to say, since the frequency of the pulseφ_(AB) becomes higher as the peak of the luminance level or of a partthereof becomes higher, the recombination speed of the overflow chargesbecomes faster in accordance with that frequency, thereby enabling theoverflow charges to be efficiently extinguished.

What we claim is:
 1. An image recording system comprising:(a) aphotosensing part for converting an optical image into an electricalsignal; (b) combining means for combining a part of the electricalsignal converted by said photosensing part with a signal opposite inpolarity to said electrical signal, said combining means having at leasttwo operation modes; (c) recording means for recording a signalrepresenting a still picture in response to said electrical signalconverted by said photosensing part; (d) trigger means for allowing saidrecording means to selectively record a signal representing a stillpicture; and (e) control means for controlling said combining means inresponse to an output of said trigger means.
 2. An image pickupapparatus according to claim 1, further including a clock signal sourcefor generating a signal to synchronously drive said recording means. 3.An image pickup apparatus according to claim 2, wherein said controlmeans is connected to said clock signal source and controls theoperation mode of said combining means for a predetermined periodsynchronized with an output of said clock signal source after the outputfrom said trigger means has been obtained.
 4. An image pickup apparatusaccording to claim 3, wherein said control means makes said recombiningmeans operative only for a predetermined field interval synchronizedwith the output of said clock signal source after the output from saidtrigger means is obtained.
 5. An image pickup apparatus according toclaim 1, wherein said combining means supplies a periodic alternatingpulse to at least a portion of said photosensing part.
 6. An imagepickup apparatus according to claim 1, wherein said recording meansrecords one picture plane with respect to said electrical signal at apredetermined timing in response to the output of said trigger means,and wherein said combining means is made inoperative by said controlmeans at least during this recording.
 7. An image pickup apparatusaccording to claim 1, wherein said recording means records one pictureplane in response to said electrical signal at a predetermined timing inresponse to the output of said trigger means, and wherein said combiningmeans is made inoperative by said control means for a predetermined timeafter this recording is started.
 8. An image pickup apparatus accordingto claim 1, further including a shutter for blocking the light incidenton said photosensing part at a predetermined timing in response to theoutput of said trigger means.
 9. An image pickup apparatus according toclaim 8, wherein said control means makes said combining meansinoperative at least while said shutter is closed.
 10. An image pickupapparatus according to claim 8, wherein said control means makes saidcombining means inoperative for a predetermined interval after theclosing of said shutter is started.
 11. An image pickup apparatusaccording to claim 1, further including (a) object information formingmeans for forming information with respect to the brightness of theobject the light from which is incident on said photosensing part; and(b) second control means for controlling the operation mode of saidcombining means in response to an output of said object informationforming means.
 12. An image pickup apparatus comprising:(a) aphotosensing part for converting an optical image into an electricalsignal; (b) combining means for combining a part of said electricalsignal converted by said photosensing part with a signal opposite inpolarity to said electrical signal; (c) a clock signal source forsynchronously driving said photosensing part and said combining meanswith a predetermined timing signal; (d) trigger means for forming atrigger signal; (e) control means for changing the operating state ofsaid combining means before and after an output of said trigger means isobtained.
 13. An image pickup apparatus according to claim 12, whereinsaid combining means supplies a periodic alternating pulse having apredetermined level to a at least part of said photosensing part.
 14. Animage pickup apparatus according to claim 12, further includingrecording means for recording a signal in response to said electricalsignal converted by said photosensing part synchronously with the outputof said clock signal source.
 15. An image pickup apparatus according toclaim 14, wherein said recording means records one picture plane inresponse to said electrical signal at a predetermined timing in responseto the output of said trigger means, and wherein said combining means ismade inoperative by said control means at least during this recording.16. An image pickup apparatus according to claim 14, wherein saidrecording means records one picture plane in response to said electricalsignal at a predetermined timing in response to the output of saidtrigger means, and wherein said combining means is mode inoperative bysaid control means for a predetermined time after this recording isstarted.
 17. An image pickup apparatus according to claim 12, furtherincluding a shutter for blocking the light incident on said photosensingpart at a predetermined timing in response to the output of said triggermeans.
 18. An image pickup apparatus according to claim 17, wherein saidcontrol means makes said combining means inoperative at least while saidshutter is closed.
 19. An image pickup apparatus according to claim 17,wherein said control means makes said combining means inoperative for apredetermined interval after the closing operation of said shutter isstarted.
 20. An image pickup apparatus according to claim 12, whereinsaid control means makes said combining means operative only for apredetermined field interval synchronized with the output of said clocksignal source after the output from said trigger means was obtained. 21.An image pickup apparatus according to claim 12, further including (a)object information forming means for forming information with respect tothe brightness of the object the light from which is incident on saidphotosensing part; and (b) second control means for controlling theoperating state of said combining means in response to an output of saidobject information forming means.
 22. An image pickup apparatuscomprising:(a) a photosensing part for converting an optical image intoan electrical signal; (b) combining means for combining a part of saidelectrical signal converted by said photosensing part with a signalopposite in polarity to said electrical signal; (c) object informationforming means for forming information with respect to brightness of anobject the light from which is incident on said photosensing part; and(d) control means for controlling the operating state of said combiningmeans in response to said information.
 23. An image pickup apparatusaccording to claim 22, wherein said object information forming meansforms information with respect to the average level of the brightness ofthe object.
 24. An image pickup apparatus according to claim 22, whereinsaid object information forming means forms information with respect tothe peak value of the brightness of the object.
 25. An image pickupapparatus according to claim 22, wherein said object information formingmeans forms information with respect to the brightness of the object inresponse to the signal from said photosensing part.
 26. An image pickupapparatus according to claim 22, wherein said object information formingmeans includes a device, which receives the light from said object andforms information with respect to brightness of the object, providedseparately from said photosensing part.
 27. An image pickup apparatusaccording to claim 22, wherein said combining means supplies a periodicalternating pulse to at least a part of said photosensing part.
 28. Animage pickup apparatus according to claim 27, wherein said secondcontrol means controls the frequency of the alternating pulse from saidcontinuing means in response to the output of said object informationforming means.
 29. An apparatus comprising:(a) supply means forsupplying power; (b) a converting part for converting incident radiationinto an electrical signal; (c) preventing means for preventing anoverflow of said electrical signal at said converting part according topower supplied thereto by said supply means, said preventing meanshaving a first mode of preventing the overflow and a second mode lowerin power consumption than said first mode; (d) change-over means formaking a change-over to determine whether a signal corresponding to saidelectrical signal is output to the outside of said apparatus duringoperation of the apparatus; and (e) a control means, responsive to theoperation of said change-over means for making a change-over between thetwo modes of said preventing means.
 30. An apparatus according to claim29, wherein said second mode is a mode for stopping the operation ofsaid preventing means.
 31. An apparatus according to claim 29, whereinthe signal corresponding to said electrical signal transmitted throughsaid change-over means is recorded by external recording means.
 32. Anapparatus according to claim 31 further comprising:second control meansfor operating said change-over means so that said electrical signal isoutput to the outside of said apparatus upon conditioning of therecording means for recording and said electrical signal is not outputto the outside of said apparatus when the recording means is notconditioned for recording.
 33. An apparatus according to claim 29,wherein said control means operates said preventing means in said firstmode when said electricalvl signal to be transmitted through saidchange-over means is obtained by said converting part.
 34. An apparatusaccording to claim 29, wherein said control means operates saidpreventing means in said second mode when said electrical signal isoutput to the outside of said apparatus through said change-over means.35. An apparatus according to claim 29, wherein said preventing meansincludes combining means for extinguishing said electrical signal toprevent the overflow.
 36. An image pickup apparatus comprising:(a)supply means for supplying power; (b) a converting part for convertingincident radiation into an electrical signal; (c) read-out means forreading out said electrical signal from said converting part at apredetermined interval; (d) preventing means for preventing an overflowof said electrical signal at said converting part according to asupplied power supplied thereto by said supply means, said preventingmeans having a first mode of preventing the overflow and a second modelower in power consumption than said first mode; (e) processing meansfor processing said electrical signal read out by said read-out means;and (f) control means for making a change-over between the modes of saidpreventing means according to the processing state of said processingmeans.
 37. An image pickup apparatus according to claim 36, wherein saidsecond mode is a mode of stopping the operation of said preventingmeans.
 38. An image pickup apparatus according to claim 36, wherein saidprocessing means is a recording unit of recording a signal correspondingto said electrical signal read out by said read-out means.
 39. An imagepickup apparatus according to claim 38, wherein said control meansoperates said preventing means in the first mode when a signal to berecorded by said recording means is obtained at said converting meansand operates said preventing means in the second mode when a signalwhich is not recorded by said recording means is obtained at saidconverting part.
 40. An image pickup apparatus according to claim 36,wherein said preventing means includes combining means for extinguishingsaid electrical signal to prevent the overflow.
 41. An image pickupapparatus comprising:(a) supply means for supplying power; (b)converting means for converting an incident image into an electricalsignal; (b) preventing means for preventing an overflow of saidelectrical signal at said converting part according to power suppliedthereto by said supply means, said preventing means having a first modeof preventing the overflow and a second mode lower in power consumptionthan said first mode, said preventing means including combining meansfor extinguishing said electrical signal to prevent the overflow; (d)object information forming means for forming information with respect tothe brightness of an object the image of which is projected onto saidconverting means as incident light; and (e) control means forcontrolling the mode of operation of said preventing means on the basisof said information.
 42. An image pickup apparatus according to claim41, wherein said object information forming means forms information withrespect to the average level of the brightness of the object.
 43. Animage pickup apparatus according to claim 41, wherein said objectinformation forming means forms information with respect to the peakvalue of the brightness of the object.
 44. An image pickup apparatusaccording to claim 41, wherein said object information forming meansforms information with respect to the brightness of said object on thebasis of said electrical signal converted by said converting means. 45.An image pickup apparatus according to claim 41, wherein said combiningmeans of said preventing means includes:means for combining a part ofsaid electrical signal converted by said converting means with anelectrical signal which has an opposite characteristic to saidelectrical signal.
 46. An image pickup apparatus according to claim 45,wherein said combining means supplies a periodically alternating pulseto said converting means.